System and method for improving the operation of an aircraft

ABSTRACT

Systems and methods of improving the operation of an aircraft during flight are disclosed. In one embodiment, the method comprises deploying spoilers as the speed of the aircraft approaches the maximum operating Mach number of the aircraft, and keeping the spoilers deployed when the speed of the aircraft is substantially at the maximum operating Mach number.

CROSS REFERENCE TO RELATED APPLICATIONS AND CLAIM OF PRIORITY

This application is a continuation of U.S. patent application Ser. No.16/364,687 filed on Mar. 26, 2019 and incorporated herein by reference,which claims priority to U.S. provisional patent application No.62/649,875 filed on Mar. 29, 2018, the entire contents of which arehereby incorporated by reference.

TECHNICAL FIELD

The disclosure relates generally to aircraft, and more particularly toimproving the operation of aircraft.

BACKGROUND

As an aircraft in flight approaches the speed of sound, air flowing overlow-pressure areas of its surface can locally reach the speed of soundand thereby form undesirable shock waves which can affect the stabilityof the aircraft. The indicated airspeed can change with ambienttemperature, which in turn changes with altitude. Therefore, theindicated airspeed is not always an adequate indication for warning thepilot of an impending problem. The Mach number can be more useful andsome high-speed aircraft are limited to a maximum operating Mach numberM_(MO). The M_(MO) serves as an upper limit for the allowable cruisespeed of the aircraft. For the sake of performance and marketability, itcan be desirable for some high-speed aircraft to have a relatively highM_(MO).

SUMMARY

In one aspect, the disclosure describes a method of improving thestability of an aircraft during flight. The method comprises:

using data indicative of a speed of the aircraft during flight,automatically causing a deployment of spoilers movably attached to wingsof the aircraft when the speed of the aircraft is equal to or exceeds aspoiler-deployment trigger speed that is lower than a maximum operatingMach number of the aircraft; and

causing the spoilers to remain deployed when the speed of the aircraftis between the spoiler-deployment trigger speed and the maximumoperating Mach number of the aircraft.

The spoilers may include a first spoiler of a port-side wing and acounterpart second spoiler of a starboard-side wing.

Causing the deployment of the spoilers may include causing the first andsecond spoilers to be deployed to a same deployment amount. The samedeployment amount may be about 12.5% of a maximum deployment amount ofthe spoilers. The same deployment amount may be less than 30% of amaximum deployment amount of the spoilers. The same deployment amountmay be between 6% and 20% of a maximum deployment amount of thespoilers. The same deployment amount may be about 5 degrees. The samedeployment amount may be less than 15 degrees. The same deploymentamount may be between 3 and 10 degrees.

The method may comprise automatically causing the deployment of thespoilers when the speed of the aircraft is equal to or exceeds thespoiler-deployment trigger speed and when the aircraft is in a cruisephase of flight.

The method may comprise, after causing the spoilers to remain deployed,causing the spoilers to fully retract when the speed of the aircraft isbelow the spoiler-deployment trigger speed.

The spoiler-deployment trigger speed may be between 0.25% and 12% of themaximum operating Mach number of the aircraft. The spoiler-deploymenttrigger speed may be between 0.5% and 5% of the maximum operating Machnumber of the aircraft.

Automatically causing the deployment of spoilers may comprise causingsymmetric deployment of one or more spoilers of a port-side wing of theaircraft and one or more spoilers of a starboard-side wing of theaircraft.

The method may comprise keeping the spoilers deployed to a fixeddeployment amount while the speed of the aircraft is between thespoiler-deployment trigger speed and the maximum operating Mach numberof the aircraft.

Embodiments can include combinations of the above features.

In another aspect, the disclosure describes a system for improving thestability of an aircraft during flight. The system comprises one or morecontrollers for controlling an actuation of a plurality of spoilersmovably attached to wings of the aircraft. The one or more controllersare configured to:

using data indicative of a speed of the aircraft during flight,automatically command a deployment of the spoilers when the speed of theaircraft is equal to or exceeds a spoiler-deployment trigger speed thatis lower than a maximum operating Mach number of the aircraft; and

cause the spoilers to remain deployed when the speed of the aircraft isbetween the spoiler-deployment trigger speed and the maximum operatingMach number of the aircraft.

The spoilers may include a first spoiler of a port-side wing and acounterpart second spoiler of a starboard-side wing.

Automatically commanding the deployment of the spoilers may includecommanding a deployment of the first and second spoilers to a samedeployment amount.

The same deployment amount may be about 12.5% of a maximum deploymentamount of the spoilers. The same deployment amount may be less than 30%of a maximum deployment amount of the spoilers. The same deploymentamount may be between 6% and 20% of a maximum deployment amount of thespoilers. The same deployment amount may be about 5 degrees. The samedeployment amount may be less than 15 degrees. The same deploymentamount may be between 3 and 10 degrees.

The one or more controllers may be configured to automatically commandthe deployment of the spoilers when the speed of the aircraft is equalto or exceeds the spoiler-deployment trigger speed and when the aircraftis in a cruise phase of flight.

The one or more controllers may be configured to, after causing thespoilers to remain deployed, cause the spoilers to fully retract whenthe speed of the aircraft is below the spoiler-deployment trigger speed.

The spoiler-deployment trigger speed may be between 0.25% and 12% of themaximum operating Mach number of the aircraft. The spoiler-deploymenttrigger speed may be between 0.5% and 5% of the maximum operating Machnumber of the aircraft.

Automatically commanding the deployment of spoilers may comprisecommanding symmetric deployment of one or more spoilers of a port-sidewing of the aircraft and one or more spoilers of a starboard-side wingof the aircraft.

The one or more controllers may be configured to cause keeping thespoilers deployed to a fixed deployment amount while the speed of theaircraft is between the spoiler-deployment trigger speed and the maximumoperating Mach number of the aircraft.

Embodiments can include combinations of the above features.

In a further aspect, the disclosure describes an aircraft comprising asystem as disclosed herein.

In a further aspect, the disclosure describes a method of improving thestability of an aircraft during flight. The method comprises:

deploying spoilers movably attached to wings of the aircraft as a speedof the aircraft approaches a maximum operating Mach number of theaircraft; and

keeping the spoilers deployed when the speed of the aircraft issubstantially at the maximum operating Mach number of the aircraft.

Deploying the spoilers may comprise deploying one or more spoilers of aport-side wing of the aircraft and one or more spoilers of astarboard-side wing of the aircraft to a same deployment amount.

The same deployment amount may be about 5 degrees. The same deploymentamount may be between 3 and 10 degrees.

The method may comprise keeping the spoilers deployed to a fixeddeployment amount while the speed of the aircraft is substantially atthe maximum operating Mach number of the aircraft.

Embodiments can include combinations of the above features.

In a further aspect, the disclosure describes a method of improving theoperation of an aircraft during flight. The method comprises:

using data indicative of a speed of the aircraft during flight,automatically causing a deployment of flight control surfaces movablyattached to wings of the aircraft when the speed of the aircraft isequal to or exceeds a deployment trigger speed that is lower than amaximum operating Mach number of the aircraft; and

causing the flight control surfaces to remain deployed when the speed ofthe aircraft is between the deployment trigger speed and the maximumoperating Mach number of the aircraft.

The flight control surfaces may include a first flight control surfaceof a port-side wing and a counterpart second flight control surface of astarboard-side wing.

Causing the deployment of the flight control surfaces may includecausing the first and second flight control surfaces to be deployed to asame deployment amount.

The method may comprise automatically causing the deployment of theflight control surfaces when the speed of the aircraft is equal to orexceeds the deployment trigger speed and when the aircraft is in acruise phase of flight.

The method may comprise, after causing the flight control surfaces toremain deployed, causing the flight control surfaces to fully retractwhen the speed of the aircraft is below the deployment trigger speed.

Automatically causing the deployment of flight control surfaces maycomprise causing symmetric deployment of one or more flight controlsurfaces of a port-side wing of the aircraft and one or more flightcontrol surfaces of a starboard-side wing of the aircraft.

The method may comprise keeping the flight control surfaces deployed toa fixed deployment amount while the speed of the aircraft is between thedeployment trigger speed and the maximum operating Mach number of theaircraft.

The flight control surfaces may include one or more of the following:spoilers, flaps and ailerons.

Embodiments can include combinations of the above features.

Further details of these and other aspects of the subject matter of thisapplication will be apparent from the detailed description includedbelow and the drawings.

DESCRIPTION OF THE DRAWINGS

Reference is now made to the accompanying drawings, in which:

FIG. 1 is a top plan view of an exemplary aircraft comprising a systemfor improving the operation of the aircraft;

FIG. 2 is a schematic representation of an exemplary system forimproving the operation of the aircraft of FIG. 1 ;

FIG. 3 is a flow diagram illustrating an exemplary method for improvingthe operation of the aircraft of FIG. 1 ;

FIG. 4 is a flow diagram illustrating another exemplary method forimproving the operation of the aircraft of FIG. 1 ;

FIG. 5 is a table illustrating different spoiler-deployment triggerspeeds and corresponding maximum operating Mach numbers of the aircraftof FIG. 1 for different altitude ranges;

FIG. 6A is a top plan view of part of the aircraft of FIG. 1 showingareas of flow separation when the aircraft is in a side slip conditionwith spoilers of the aircraft not deployed; and

FIG. 6B is a top plan view of the part of the aircraft of FIG. 1 showingareas of flow separation when the aircraft is in a side slip conditionwith the spoilers of the aircraft deployed.

DETAILED DESCRIPTION

The following description relates to methods and system for improvingthe operation of an aircraft during relatively high-speed flight. Invarious embodiments, the methods and systems disclosed herein make useof a relatively small and symmetric flight control surfacedeployment/actuation in order to improve the flow conditions over thewings of an aircraft and allow for the use of a higher maximum operatingMach number (M_(MO)) for the aircraft than would otherwise becertifiable without such deployment of the flight control surfaces. Invarious embodiments, such deployment of the flight control surfaces mayimprove static lateral stability, reduce drag and/or increase a buffetboundary of the aircraft during flight.

In some embodiments, the method comprises: deploying spoilers (and/orother flight control surfaces) movably attached to wings of the aircraftas a speed of the aircraft approaches a maximum operating Mach number ofthe aircraft; and keeping the spoilers (and/or other flight controlsurfaces) deployed when the speed of the aircraft is substantially atthe M_(MO) of the aircraft. The M_(MO) serves as an upper limit for theallowable cruise speed of an aircraft and is the aircraft's maximumcertified cruising Mach number. The M_(MO) is defined in regulations ofapplicable certification authorities such as the Federal AviationAdministration (FAA) of the United States for example and corresponds toan operating limit Mach number that requires, for example, that staticlateral stability of an aircraft be, at worst, neutral at M_(MO). TheM_(MO) also corresponds to a speed above which one or more regulationsof an applicable certification authority would not be complied with. Insome situations, an excursion beyond the M_(MO), could cause inducedflow separation of boundary layer air over the wings of an airplanewhich could lead to lateral instability, buffeting and increased drag.

The static lateral stability of an aircraft is a fundamental aerodynamicproperty associated with the aircraft configuration, and is linked tothe wing design. For a stable configuration in a side slip condition forexample, the leading wing should produce higher lift than the trailingwing and control forces (e.g., using aileron, rudder) can be applied ina conventional sense to counter this effect. However, in some situationsand for some wing designs, it was observed that negative static lateralstability, or opposite roll response to what is expected, can manifestitself at a high

Mach number as a result of shock-induced flow separation on the wing. Insuch conditions, the leading wing in a side slip produces strongershocks while the trailing wing sees a reduction in shock strength. Thestronger shocks increase the flow separation on the leading wing therebyreducing lift instead of increasing lift. Conversely, the trailing wingmay yield less lift reduction in side slip as weaker shocks may resultin reduced flow separation. Such flow characteristics can thereforeresult in a behaviour (e.g., rolling motion) of the aircraft that iscounterintuitive to the pilots. The shock-induced flow separation canpotentially also cause buffeting and be a source of increased aircraftdrag.

The use of a relatively small symmetrical control surface (e.g.,multi-function spoiler, flap, aileron and/or spoileron) deflection abovea certain speed of the aircraft was found to, in some situations,mitigate the instability and/or other negative effect(s) caused by theshock-induced flow separation in specific areas of the wing withoutprohibitively increasing drag. Aspects of various embodiments aredescribed through reference to the drawings.

FIG. 1 is a top plan view of an exemplary aircraft 10, which comprisessystem 12 for improving the operation (e.g., static lateral stability,buffet boundary, drag) of aircraft 10 at relatively high speed such asnear and at M_(MO). Aircraft 10 may be any type of aircraft such ascorporate (e.g., business jet), private, commercial and passengeraircraft suitable for civil aviation. For example, aircraft 10 may be anarrow-body, twin-engine jet airliner or may be an ultra-long rangebusiness jet. Aircraft 10 may be a fixed-wing aircraft.

Aircraft 10 may comprise wings 14A and 14B (also referred generallyherein as “wings 14”), fuselage 15, one or more engines 16 and empennage18. One or more of engines 16 may be mounted to fuselage 15.Alternatively, or in addition, one or more of engines 16 may be mountedto wings 14. Wing 14A may be a port-side (i.e., left) wing relative tolongitudinal axis LA of fuselage 15. Wing 14B may be a starboard-side(i.e., right) wing relative to longitudinal axis LA of fuselage 15.Wings 14 may each include one or more flight control surfaces such asaileron(s) 20, leading edge slat(s) 22, spoilers 24A, 24B and trailingedge flap(s) 26. Leading edge slats 22 and trailing edge flaps 26 may beconsidered “high-lift” flight control surfaces that may be deployed toincrease the amount of lift generated by wings 15 during phase(s) offlight requiring increased lift.

Spoilers 24 can also sometimes be called “lift spoilers” or “liftdumpers” and are flight control surfaces/devices normally intended toreduce an amount of lift produced by wings 14 during flight or landingof aircraft 10. Spoilers 24 may comprise plates/surfaces disposed on thetop side of wings 14 and that can be deflected or extended into theairflow to spoil the airflow. Spoilers 24 may be configured to reducelift as well as increase drag on landing of aircraft 10 for example.Spoilers 24 may be deployed at controlled angles (typically expressed indegrees) during flight to increase a descent rate or control roll.Spoilers 24A may be movably mounted to port-side wing 14A and spoilers24B may be movably mounted to starboard-side wing 14B. In someembodiments, some of spoilers 24 (e.g., multi-function spoilers,spoilerons) may be deployed at controlled angles during flight toincrease descent rate or control roll while other spoilers 24 (e.g.,ground spoilers) may be fully deployed immediately on landing to greatlyreduce lift and increase drag. In some embodiments of aircraft 10,multi-function spoilers may be disposed outboard of ground spoilers onrespective wings 14A, 14B.

FIG. 1 schematically shows system 12 superimposed on aircraft 10 wheresystem 12 may be associated with spoilers 24A movably attached toport-side wing 14A and also with spoilers 24B movably attached tostarboard-side wing 14B. As illustrated in FIG. 1 , system 12 may beassociated with some or all of spoilers 24 of each wing 14. For example,system 12 may be associated with both inboard and outboard spoilers 24of each wing 14 relative to fuselage 14. However, it is understood thatin some embodiments, system 12 could be associated with only one or some(e.g., inboard or outboard) spoilers 24 of each wing 14. For example, insome embodiments, system 12 may be associated with inboardmulti-function spoilers located laterally between ground spoilers andoutboard multi-function spoilers.

Even though the present disclosure relates mainly to the use of spoilerdeployment for improving the operation of aircraft 10 at relatively highspeed, it is understood that, in various situations and wing designs,the deployment of other flight control surfaces could also be used tomitigate the effects of flow separation in order to achieve someimprovement in static lateral stability, buffet boundary and/or dragreduction. The selection of which flight control surface(s) to deploymay be based on the characteristics of wings 14 and the location(s) offlow separation on wings 14. Accordingly, it is understood that system12 may be associated with other flight control surfaces such as trailingedge flaps 26 and/or ailerons 20 that are movably attached to wings 14.

FIG. 2 is a schematic representation of an exemplary system 12 forimproving the operation (e.g., static lateral stability, increase inbuffet boundary, drag reduction) of aircraft 10. In some embodiments,system 12 may be used specifically during a cruise phase of flight ofaircraft 10 at speeds approaching M_(MO) and at M_(MO). System 12 isillustrated in FIG. 2 together with only one spoiler 24 of each wing 14for simplicity but it is understood that system 12 can be associatedwith some or all spoilers 24 of both wings 14 and/or with other flightcontrol surfaces.

System 12 may comprise one or more actuators 30A operatively coupled tocause actuation of spoiler(s) 24A of port-side wing 14A based oninstructions generated by one or more controllers 32. Similarly, system12 may comprise one or more actuators 30B operatively coupled to causeactuation of spoiler(s) 24B of starboard-side wing 14B based oninstructions generated by controller(s) 32. It is understood thataspects of the present disclosure may also be used with aircraft 10having different spoiler configurations and actuation systems than thoseshown herein. For example, it is understood that, in some embodiments, acommon controller 32 may control the actuation of both spoiler(s) 24Aand spoilers 24B. Alternatively, in some embodiments, system 12 maycomprise separate dedicated controllers 32 respectively associated withspoiler(s) 24A and spoiler(s) 24B. Actuators 30A, 30B, also referredgenerally herein as “actuators 30”, may each comprise a suitable (e.g.,pneumatic, hydraulic and electric) actuator for transmitting anactuation force to respective spoilers 24.

System 12 may comprise one or more controllers 32 (referred below in thesingular). Controller 32 may be operatively coupled to spoilers 24 viaactuators 30 for commanding actuation of spoilers 24. Controller 32 maybe operatively coupled to also command the actuation of other flightcontrol surfaces of aircraft 10 in some embodiments. Controller 32 maybe operatively coupled to other avionics component(s) or otherwiseconfigured to receive commands from a pilot of aircraft 10 directly orindirectly, or receive commands from an auto-flight system of aircraft10. Controller 32 may also be operatively coupled to receive data 34directly or indirectly from one or more suitable data sources such assensors 36 or other avionics components. Controller 32 may beoperatively coupled to a control input device located in a cockpit ofaircraft 10 and actuatable by the pilot(s) to permit manually commandedactuation of spoilers 24 to different deployment settings.

Controller 32 may comprise one or more data processors and one or morecomputer-readable memories storing machine-readable instructionsexecutable by the data processor(s) and configured to cause controller32 to perform a series of steps so as to implement acomputer-implemented process such that instructions, when executed bysuch data processor(s) or other programmable apparatus, can cause thefunctions/acts specified in the methods described herein to be executed.Memory(ies) can comprise any storage means (e.g. devices) suitable forretrievably storing machine-readable instructions executable by the dataprocessor(s) of controller 32.

Various aspects of the present disclosure can be embodied as systems,devices, methods and/or computer program products. Accordingly, aspectsof the present disclosure can take the form of an entirely hardwareembodiment, an entirely software embodiment or an embodiment combiningsoftware and hardware aspects. Furthermore, aspects of the presentdisclosure can take the form of a computer program product embodied inone or more non-transitory computer readable medium(ia) having computerreadable program code embodied thereon. The computer program productcan, for example, be executed by controller 32 to cause the execution ofone or more methods disclosed herein in entirety or in part. It isunderstood that, based on the present disclosure, one skilled in therelevant arts could readily write computer program code for implementingthe methods disclosed herein.

Controller 32 may be operatively coupled to spoilers 24 for commandingdeployment and retraction of spoilers 24 in unison and cause symmetricdeployment of spoilers 24A and 24B between port-side wing 14A andstarboard-side wing 14B. In various embodiments, controller 32 may bededicated to the actuation of spoilers 24 or may be configured to carryout other tasks as well. In some embodiments, controller 32 may compriseor be integrated with a flight control computer (FCC) of a fly-by-wiresystem of aircraft 10 for example. Controller 32 may be configured toautomatically command deployment and retraction of spoilers 24 based ondata 34 and one or more suitable control laws. The methods disclosedherein may be implemented on new aircraft designs or retrofitted to anexisting aircraft without making significant structural modifications tosuch existing aircraft.

Data 34 may comprise information indicative of a current state oroperating condition of aircraft 10. Data 34 may comprise one or moresubstantially real-time stored or sensed parameters acquired viasuitable sensor(s) 36, one or more computed/derived parameters and oneor more predetermined threshold values for example. In variousembodiments, data 34 may comprise current speed (e.g., airspeed, Machnumber), phase of flight, aircraft weight, altitude, a deployment angleα of spoilers 24 and predetermined threshold values (e.g., limits,altitude ranges, spoiler-deployment trigger speeds, spoiler-retractiontrigger speeds, M_(MO)). Some or all of data 34 may be available tocontroller 32 to permit controller 32 to perform the tasks describedherein. It is understood that some of data 34 could instead becomputed/derived by controller 32 or could be stored in memory that isaccessible by controller 32. Deployment angle α of spoilers 24 is shownin FIG. 2 relative to a fully retracted position of spoilers 24.Spoilers 24 may be actuatable between and including a fully retractedposition (i.e., α=0 degree) and a fully deployed position (e.g., α=40degrees). Spoilers 24 may be configured to be actuated to and held atintermediate positions between the fully retracted position and thefully deployed position.

FIG. 3 is a flow diagram illustrating an exemplary method 100 forimproving the operation (e.g., static lateral stability, buffetboundary, drag) of aircraft 10. Method 100 can be performed using system12 as described above or using another suitable system. Method 100 maybe computer-implemented via controller 32 for example. Method 100 may beimplemented by way of one or more control laws associated with system12. Aspects and functions of system 12 disclosed herein can also beapplicable to method 100. Method 100 may comprise: using data 34indicative of a speed of aircraft 10 during flight, automaticallycausing a deployment of flight control surfaces (e.g., spoilers 24)movably attached to wings 14 of aircraft 10 when the speed of aircraft10 is equal to or exceeds a (e.g., spoiler-) deployment trigger speedthat is lower than the M_(MO) of aircraft 10 (see block 102); andcausing the flight control surfaces (e.g., spoilers 24) to remaindeployed when the speed of aircraft 10 is between the (e.g., spoiler-)deployment trigger speed and the M_(MO) of aircraft 10 (see block 104).

In various embodiments, the flight control surfaces used in method 100may be spoilers 24, flaps 26 and/or ailerons 20. For example, in someembodiments, method 100 may deploy only (exclusively) spoilers 24 toachieve the desired operational improvement. In some embodiments, method100 may deploy only (exclusively) flaps 26 to achieve the desiredoperational improvement. In some embodiments, method 100 may deploy only(exclusively) ailerons 20 to achieve the desired operationalimprovement. In some embodiments, method 100 may deploy only(exclusively) spoilerons to achieve the desired operational improvement.In some embodiments, method 100 may make use of simultaneous deploymentof one or more types of flight control surfaces to achieve the desiredoperational improvement based on the location and characteristics of theflow separation on wings 14. In various embodiments of method 100, theflight control surface deployment may be symmetrical between port-sidewing 14A and starboard-side wing 14B.

Even though aspects of method 100 described below are described inrelation to spoilers 24, it is understood that such aspects can beapplicable to other types of flight control surfaces of aircraft 10.

In some embodiments, the automatic deployment (and subsequentretraction) of spoilers 24 may be carried out without explicitinstruction from the pilot(s) of aircraft 10. For example, the automaticdeployment (and subsequent retraction) of spoilers 24 could be carriedout without pilot input and be transparent to the pilot(s) of aircraft10.

In various embodiments, all or only some of spoilers 24 may be deployedas part of method 100 to improve the operation (e.g., lateral stability,buffet boundary, drag) of aircraft 10. In some embodiments, onlymulti-function spoilers of each wing 14 may be deployed as part ofmethod 100 to improve the operation of aircraft 10 while ground spoilersremain retracted. In some embodiments, only one or more inboardmulti-function spoilers of each wing 14 may be deployed as part ofmethod 100 to improve the static lateral stability of aircraft 10 whileground spoilers and other outboard multi-function spoilers remainretracted. The inboard multi-function spoilers may be disposed betweenthe outboard multi-function spoilers and the ground spoilers along aspanwise direction of each wing 14.

In various embodiments, the deployment of spoilers 24 may includedeploying one or more spoilers 24A of port-side wing 14A of aircraft 10and one or more counterpart spoilers 24B of starboard-side wing 14B ofaircraft to a same deployment amount (e.g., by the same deployment angleα shown in FIG. 2 ). Accordingly, spoiler deployment may be symmetricalbetween port-side wing 14A and starboard-side wing 14B.

The amount of spoiler deployment required to improve the operation ofaircraft 10 may be relatively small and may depend on the specificaircraft and the effect desired. The selection of which spoiler(s) 24 todeploy and by what deployment angle α may be dependent on the specificaircraft and on the location and size of the shock-induced flowseparation region on one or both wings 14. In some situations, since theamount of spoiler deployment required to improve the operation ofaircraft 10 at high speed may be relatively small, the spoilerdeployment may consequently not prohibitively increase drag. In somesituation, the mitigation of the effects of shock-induced flowseparation provided by the deployment of spoilers 24 may besubstantially drag neutral (or drag reducing) under the applicableoperating conditions. For example, even though the slightly deployedspoilers 24 would extend into the air flow over the wings 14, theslightly deployed spoilers 24 would also, in some embodiments, reduceshock strength in some regions and hence reduce the shock-induced flowseparation in one or more critical areas of one or both wings 14.Furthermore, the spoiler deployments can be tailored in such fashion asto modify the span-wise distribution of lift on the wing 14 in theseflow conditions thereby reducing the induced drag of aircraft 10.

In some embodiments, the required spoiler deployment angle α may bepredetermined experimentally or by modeling/simulation based on theoperating conditions and applicable performance requirements. In someembodiments, the deployment angle α for method 100 may be afixed/constant (i.e., non-variable) value that is triggered based onspeed of aircraft, and optionally also based on the phase of flight,irrespective of other parameters. Accordingly, the same fixed value ofdeployment angle α may be used repeatedly at the applicable times duringa same flight and during different flights.

In some embodiments, once spoilers 24 have been deployed in method 100,they may not be actively controlled/modulated during maneuvers based onany other parameter(s). For example, the deployment of spoilers 24 maybe triggered at the spoiler-deployment trigger speed and then keptdeployed (i.e., held) to the fixed deployment amount while the speed ofaircraft 10 is between the spoiler-deployment trigger speed and theM_(MO) of aircraft 10. Spoilers 24 may also be kept deployed (i.e.,held) while the speed of aircraft 10 is substantially at M_(MO) ofaircraft 10.

Method 100 may also comprise, after causing spoilers 24 to remaindeployed at the fixed deployment angle α at the applicable speed(s),causing spoilers 24 to automatically fully retract when the speed ofaircraft 10 is below the spoiler-deployment trigger speed. In someembodiments, a spoiler-retraction trigger speed may be used to triggerthe retraction of spoilers 24. Such spoiler-retraction trigger speed maybe slightly lower than the spoiler-deployment trigger speed to provide adeadband and prevent oscillation of spoilers 24 around the applicabletrigger speeds.

In some embodiments of method 100, a spoiler deployment angle α of about5 degrees may provide some operational improvement. In a case where amaximum deployment angle of the applicable spoilers 24 may be about 40degrees, a 5-degree deployment may correspond to about 12.5% of themaximum deployment angle of the applicable spoilers 24. In someembodiments, a suitable spoiler deployment angle α may be between about3 degrees and about 10 degrees. In some embodiments, a suitable spoilerdeployment angle α may be less than about 10 degrees. In someembodiments, a suitable spoiler deployment angle α may be less thanabout 15 degrees. In terms of a percentage of a maximum deploymentamount of the applicable spoilers, a suitable spoiler deployment amountfor method 100 may be between about 6% and about 20% of the maximumdeployment amount of the applicable spoilers 24. In some embodiments, asuitable spoiler deployment amount for method 100 may be between about10% and about 15% of the maximum deployment amount of the applicablespoilers 24. In some embodiments, a suitable spoiler deployment amountmay be less than about 20% of the maximum deployment amount of theapplicable spoilers 24. In some embodiments, a suitable spoilerdeployment amount may be less than about 30% of the maximum deploymentamount of the applicable spoilers 24.

As explained above, the automatic deployment of spoilers 24 may betriggered by the speed of the aircraft being equal to or exceeding thespoiler-deployment trigger speed. However, another optional conditionmay be based on a phase of flight of aircraft 10. For example, method100 may be used during a cruise phase of flight so as to allow for theuse of a higher M_(MO) for aircraft 10 than would otherwise be mandatedwithout such deployment of spoilers 24. In reference to FIG. 2 , data 34may comprise data representative of the current phase of flight ofaircraft 10.

FIG. 4 is a flow diagram illustrating another exemplary method 200 forimproving the operation (e.g., lateral stability, buffet boundary, drag)of aircraft 10. Method 200 can be performed using system 12 as describedabove or using another suitable system. Method 200 may becomputer-implemented via controller 32 for example. Method 200 may beimplemented by way of one or more control laws associated with system12. Aspects and functions of system 12 and of method 100 disclosedherein can also be applicable to method 200. Again, even though aspectsof method 200 are described in relation to spoilers 24, it is understoodthat such aspects can be applicable to other types of flight controlsurfaces. Method 200 may comprise: deploying spoilers 24 movablyattached to wings 14 of aircraft 10 as a speed of aircraft 10 approachesM_(MO) of aircraft 10 (see block 202); and keeping spoilers 24 deployedwhen the speed of aircraft 10 is substantially at M_(MO) of aircraft 10.

FIG. 5 is a table illustrating different spoiler-deployment triggerspeeds (TS1-TS3) and corresponding maximum operating Mach numbers(M_(MO) 1-M_(MO) 3) of aircraft 10 for different altitude ranges. Themethods disclosed herein may be performed at relatively high altitudeswhere M_(MO) is the limiting speed of aircraft 10. Since the stall speedof an aircraft can vary based on altitude due to changes inenvironmental conditions and to the speed of sound with altitude, it isunderstood that the M_(MO) of aircraft 10 can vary based on altitude. Inreference to FIG. 5 , altitude range A3-A4 is intended to be higher thanaltitude range A1-A2 and altitude range A5-A6 is intended to be higherthan altitude range A3-A4. Since the M_(MO) of aircraft 10 can decreasewith increasing altitude, M_(MO) 2 may be lower than M_(MO) 1 and M_(MO)3 may be lower than M_(MO) 2.

Due to the variation of M_(MO) with altitude, a differentspoiler-deployment trigger speed TS1-TS3 may be associated with eachM_(MO). The applicable spoiler-deployment trigger speed may be lowerthan its associated M_(MO). In some embodiments, the applicablespoiler-deployment trigger speed may be slightly lower than M_(MO). Insome embodiments, the spoiler-deployment trigger speed may correspond toan alternate and lower M_(MO) that would be mandated without deploymentof spoilers 24 as explained herein. For example, the spoiler-deploymenttrigger speed may correspond to a threshold speed of aircraft 10 abovewhich deployment of spoilers 24 is required to maintain a desiredlateral stability of aircraft 10. In some embodiments, thespoiler-deployment trigger speed may be within about 8% of the M_(MO) ofaircraft 10. In some embodiments, the spoiler-deployment trigger speedmay be within about 2% of the M_(MO) of aircraft 10. In someembodiments, the spoiler-deployment trigger speed may be between about0.25% and about 12% of the M_(MO) of aircraft 10. In some embodiments,the spoiler-deployment trigger speed may be between about 0.5% and about5% of the M_(MO) of aircraft 10.

Data 34 (see FIG. 2 ) may include data having the form of the table ofFIG. 5 that may be used by controller 32 to determine the applicableM_(MO) and corresponding spoiler-deployment trigger speed based on thecurrent altitude for the purpose of triggering the deployment ofspoilers 24 accordingly. It is understood that the table of FIG. 5 mayalso include corresponding spoiler-retraction trigger speed as explainedabove. The table of FIG. 5 may have the form of an electronic look-uptable available to controller 32.

FIGS. 6A and 6B are top plan views of part of aircraft 10 showingregions 38A, 38B of flow separation on wings 14A, 14B when aircraft 10is in a side slip condition with spoilers 24 of aircraft 10 not deployedin FIG. 6A and deployed to 5 degrees in FIG. 6B. The conditionsapplicable to FIGS. 6A and 6B include a speed of aircraft 10 of Mach0.900, an angle of attack of 0 degree and a side slip angle β of 2.5degrees in the direction shown in FIGS. 6A, 6B. Accordingly,starboard-side wing 14B is shown as the leading wing relative to theairflow and port-side wing 14A is shown as the trailing wing. FIGS. 6Aand 6B were generated by simulation/modeling.

Regions 38A and 38B of flow separation are shown in dark regions on topof wings 14A, 14B. In reference to FIG. 6A where spoilers 24 areretracted (α=0 degree), the size of region 38B on starboard-side wing14B is shown to be significantly larger than the size of region 38B onport-side wing 14A. Such difference in size of regions 38A, 38B can beindicative of a lift differential between wings 14A, 14B and canconsequently be a source of lateral instability of aircraft 10 in thesituation illustrated.

In reference to FIG. 6B where (e.g., inboard multi-function) spoilers 24are deployed to a deployment angle α of 5 degrees, region 38B of flowseparation on wing 14B is shown to have reduced in size due to thedeployment of spoiler(s) 24B compared to the situation of FIG. 6A.Consequently, the lift generated by wing 14B may be higher in thesituation of FIG. 6B than in the situation of FIG. 6A. Conversely,region 38A of flow separation on wing 14A is shown to have increased insize due to the deployment of spoiler(s) 24A compared to the situationof FIG. 6A. Consequently, the lift generated by wing 14A may be lower inthe situation of FIG. 6B than in the situation of FIG. 6A. The reductionin size of the region 38B combined with the increase in size of region38A can be indicative of a reduction in magnitude of the liftdifferential between wings 14A, 14B and can consequently be indicativeof the static lateral stability being improved in the situation of FIG.6B compared to the situation of FIG. 6A.

The improvement in static lateral stability was achieved by a relativelysmall symmetric deployment of spoilers 24A, 24B even though the sizes ofregions 38A, 38B was asymmetric between wings 14A, 14B. Since the smalldeployment of spoilers 24 is intended to be used at speeds above thespoiler-deployment trigger speed, it is believed that the methodsdisclosed herein would not affect a long-range cruise performance ofaircraft 10 when operating at a cruise speed that is below thespoiler-deployment trigger speed.

Referring to the reduction in size of region 38B from FIG. 6A to FIG. 6Bdue to the deployment of spoiler(s) 24B, it is believed that, in somesituations, such reduction in size of region 38B could be accompanied bya reduction in drag and increase in a buffet boundary. It is understoodthat the size and characteristics of the area(s) of flow separation canbe used to determine which flight control surface(s) would beappropriate to use to mitigate the effects of such flow separation andthereby improve the operation of aircraft 10. Mitigating the effects offlow separation may include altering a lift distribution across one orboth wings 14A, 14B by way of a relatively small but symmetricdeployment of one or more flight control surfaces of wings 14A, 14B.

The above description is meant to be exemplary only, and one skilled inthe relevant arts will recognize that changes may be made to theembodiments described without departing from the scope of the inventiondisclosed. The present disclosure may be embodied in other specificforms without departing from the subject matter of the claims. Thepresent disclosure is intended to cover and embrace all suitable changesin technology. Modifications which fall within the scope of the presentinvention will be apparent to those skilled in the art, in light of areview of this disclosure, and such modifications are intended to fallwithin the appended claims. Also, the scope of the claims should not belimited by the preferred embodiments set forth in the examples, butshould be given the broadest interpretation consistent with thedescription as a whole.

What is claimed is:
 1. A method of improving a stability of an aircraftduring flight, the method comprising: deploying spoilers movablyattached to wings of the aircraft as a speed of the aircraft approachesa maximum operating Mach number of the aircraft; and keeping thespoilers deployed when the speed of the aircraft is substantially at themaximum operating Mach number of the aircraft.
 2. The method as definedin claim 1, wherein deploying the spoilers comprises deploying one ormore spoilers of a port-side wing of the aircraft and one or morespoilers of a starboard-side wing of the aircraft to a same deploymentamount.
 3. The method as defined in claim 2, wherein the same deploymentamount is about 5 degrees.
 4. The method as defined in claim 3, whereinthe same deployment amount is between 3 and 10 degrees.
 5. The method asdefined in claim 1, comprising keeping the spoilers deployed to a fixeddeployment amount while the speed of the aircraft is substantially atthe maximum operating Mach number of the aircraft.
 6. A method ofimproving an operation of an aircraft during flight, the methodcomprising: using data indicative of a speed of the aircraft duringflight, automatically causing a deployment of flight control surfacesmovably attached to wings of the aircraft when the speed of the aircraftis equal to or exceeds a deployment trigger speed that is lower than amaximum operating Mach number of the aircraft; and causing the flightcontrol surfaces to remain deployed when the speed of the aircraft isbetween the deployment trigger speed and the maximum operating Machnumber of the aircraft.
 7. The method as defined in claim 6, wherein theflight control surfaces include a first flight control surface of aport-side wing and a counterpart second flight control surface of astarboard-side wing.
 8. The method as defined in claim 7, whereincausing the deployment of the flight control surfaces includes causingthe first and second flight control surfaces to be deployed to a samedeployment amount.
 9. The method as defined in claim 6, comprisingautomatically causing the deployment of the flight control surfaces whenthe speed of the aircraft is equal to or exceeds the deployment triggerspeed and when the aircraft is in a cruise phase of flight.
 10. Themethod as defined in claim 6, comprising, after causing the flightcontrol surfaces to remain deployed, causing the flight control surfacesto fully retract when the speed of the aircraft is below the deploymenttrigger speed.
 11. The method as defined in claim 6, whereinautomatically causing the deployment of flight control surfacescomprises causing symmetric deployment of one or more flight controlsurfaces of a port-side wing of the aircraft and one or more flightcontrol surfaces of a starboard-side wing of the aircraft.
 12. Themethod as defined in claim 6, comprising keeping the flight controlsurfaces deployed to a fixed deployment amount while the speed of theaircraft is between the deployment trigger speed and the maximumoperating Mach number of the aircraft.
 13. The method as defined inclaim 6, wherein the flight control surfaces include one or more of thefollowing: spoilers, flaps and ailerons.
 14. A system for improving astability of an aircraft during flight, the system comprising one ormore controllers for controlling an actuation of a plurality of spoilersmovably attached to wings of the aircraft, the one or more controllersbeing configured to: using data indicative of a speed of the aircraftduring flight, automatically cause a deployment of the plurality ofspoilers when the speed of the aircraft approaches a maximum operatingMach number of the aircraft; and keep the spoilers deployed when thespeed of the aircraft is substantially at the maximum operating Machnumber of the aircraft.
 15. A system for improving an operation of anaircraft during flight, the system comprising: one or more controllersfor controlling an actuation of a plurality of spoilers movably attachedto wings of the aircraft, the one or more controllers being configuredto: using data indicative of a speed of the aircraft during flight,automatically cause a deployment of flight control surfaces movablyattached to wings of the aircraft when the speed of the aircraft isequal to or exceeds a deployment trigger speed that is lower than amaximum operating Mach number of the aircraft; and cause the flightcontrol surfaces to remain deployed when the speed of the aircraft isbetween the deployment trigger speed and the maximum operating Machnumber of the aircraft.